Increase in ceramide level after application of various sizes of sphingomyelin liposomes to a cultured human skin model.

Sphingomyelin-based liposomes (SPM-L) that were sized (or not) by extrusion through a filter with pores of 100, 200, or 400 nm were applied to a three-dimensional cultured human skin model in order to evaluate which size of SPM-L was most effective at increasing its ceramide level. The diameters of the SPM-L in PBS were 102.7, 181.0, 224.0, and 380.1 nm. The diameters of the liposomes in the culture medium were 117.5, 199.2, 242.1, and 749.8 nm. The diameter of the small liposomes (<200 nm in diameter) did not change much, at least for 7 days. SPM-L in saline or culture medium were applied to the basal layer side or stratum corneum side of the cultured skin model, and ceramide II, III, V, and VI were then extracted from it. The extracted ceramide molecules were separated by HPTLC, and the concentration of each type of ceramide was quantified using a densitometer. When the small SPM-L (110 or 190 nm in diameter) were applied to the basal layer side, the levels of ceramide III and V were increased. When they were applied to the stratum corneum side, the levels of ceramide II, III, V, and VI were significantly increased compared to those of the PBS group, especially after the application of the small SPM-L (110 nm in diameter). Thus, the application of small SPM-L was useful for increasing the ceramide II, III, V, and VI levels of a cultured human skin model.

Simultaneous transport and metabolism of ethyl nicotinate in hairless rat skin after its topical application: the effect of enzyme distribution in skin.

An in vitro permeation study of ethyl nicotinate (EN) was carried out using excised hairless rat skin, and simultaneous skin transport and metabolism of the drug were kinetically followed. Fairly good steady-state fluxes of EN and its metabolite nicotinic acid (NA) through the skin were obtained after a short lag time for all the concentrations of EN applied. These steady-state fluxes were not proportional to the initial donor concentration of EN: EN and NA curves were concave and convex, respectively, which suggests that metabolic saturation from EN to NA takes place in the viable skin at higher EN application. Further permeation studies of EN or NA were then carried out on full-thickness skin or stripped skin with an esterase inhibitor to measure their permeation parameters, such as partition coefficient of EN from the donor solution to the stratum corneum and diffusion coefficients of EN and NA in the stratum corneum and the viable epidermis and dermis. Separately, enzymatic parameters (Michaelis constant K(m) and maximum metabolism rate V(max)) were obtained from the production rate of NA from different concentrations of EN in the skin homogenate. The obtained permeation and enzymatic parameters were then introduced to differential equations showing Fick's second law of diffusion in the stratum corneum and the law with Michaelis-Menten metabolism in the viable epidermis and dermis. The calculated steady-state fluxes of EN and NA by the equations were very close to the obtained data. We then measured the esterase distribution in skin microphotographically using fluorescein-5-isothiocyanate diacetate. A higher enzyme concentration was observed in the epidermal cells and near hair follicles than in the dermis. Simulation studies using the even and the partial enzyme distribution models suggested that no significant difference between the models was observed in the skin permeations of EN and NA, whereas concentration-distance profiles of EN and NA were very different. This finding suggests that the total amount of enzyme in skin which converts EN to NA is a determinant of the metabolic rate of EN in skin. The present approach is a useful tool for analyzing simultaneous transport and metabolism of many drugs, especially those showing Michaelis-Menten type-metabolic saturation in skin.

Analysis of skin permeation-enhancing mechanism of iontophoresis using hydrodynamic pore theory.

The effects of constant DC iontophoresis (0-1.5 mA/0.966 cm(2)) on the permeation of three hydrophilic compounds, antipyrine (ANP, M.W. 188.23), sucrose (SR, M.W. 342.30) and 1-kestose (KT, M.W. 506.73), through excised hairless rat skin were evaluated using hydrodynamic pore theory. The electro-osmotic flow caused by iontophoresis was measured using deuterium oxide (D(2)O). The penetration-enhancing mechanism of iontophoresis was found to increase solvent flow through electro-osmosis and pore enlargement and/or new pore production in the skin barrier, together with enhancement of electrochemical potential difference across the skin. These effects were closely related to the strength of the current applied. The electro-osmotic flow of D(2)O (J(D(2)O)) greatly enhanced the skin permeation clearance of all hydrophilic penetrants (CL(drug)). Pore production was classified into reversible and irreversible processes, which resulted from lower (0-0.5 mA/0.966 cm(2)) and higher (0.5-1. 5 mA/0.966 cm(2)) currents, respectively. Thus, the enhancing effects of iontophoresis on skin permeation of nonionic hydrophilic compounds can be explained by increase in pore size and higher solvent flow.

Potential usefulness of solubility index for prediction of the skin permeation rate of 5-ISMN from pressure-sensitive adhesive tape.

Skin permeation of 5-ISMN from pressure sensitive adhesive (PSA) tape was evaluated using thermodynamic activity of the drug in PSA. Three acrylic adhesives (Gelva 737, Gelva 1430 and Gelva 1753) were used as PSA. Since the drug activity in PSA is difficult to determine, however, a solubility index was defined. Several PSA tapes containing different amounts of 5-ISMN were prepared, and heat of fusion at the dissolution of 5-ISMN in each PSA was determined by DSC. No exothermic peak was found when the drug concentration was less than the solubility in PSA, whereas the heat of fusion increased proportionally with amount of solid drug in the PSA when the drug concentration was above the solubility. The bending point in the profile of heat of fusion versus 5-ISMN content in PSA was defined as the solubility index. In vitro skin permeation was determined using excised hairless rat skin from 5-ISMN-saturated PSA tapes. The obtained skin permeation of the drug decreased with increases in the solubility index. These profiles were confirmed by a theoretical approach using the differential equation corresponding to Fick's second law of diffusion. These results suggested that the solubility index can be utilized for prediction of the skin permeability of drugs from PSA tape.

Analysis of skin disposition of flurbiprofen after topical application in hairless rats.

Cutaneous disposition of topically applied flurbiprofen (FP) was evaluated using a new in situ experimental model in hairless rats. A disk-shaped agar gel (3.85 cm in diameter and 0.5 cm in thickness) was subcutaneously implanted in the abdominal region of rats as a drug receptor, and a drug donor cell was subsequently placed above this agar gel. No significant pharmacokinetic modification of FP was observed as a result of this experimental procedure. A bolus injection and a constant intravenous infusion of FP were applied to the rats, followed by an analysis of FP levels in the plasma and agar gels. Using these results, the clearance rate of FP from the systemic circulation to the gel could be calculated. FP (1% gel formulation, 1.0 g/3.14 cm(2)) was then topically applied to the skin of these rats. From these experiments, the amount of FP that migrated from the formulation to the systemic circulation and the amount of FP that migrated directly to the agar gel across the skin, over 10 h, were separately evaluated to be 235.4 and 2.0 microg, respectively. Thus, most of the FP was absorbed into the systemic circulation. The effect of endogeneous vasoactive compounds and penetration enhancers on the FP disposition within skin was also determined. Epinephrine and bradykinin were used as vasoactive compounds that were entrapped in agar gel, and an isopropyl myristate system (IPM system) and a l-menthol-ethanol-glycerin-water system (MEGW system) were used as enhancers in the formulation. Epinephrine enhanced the direct delivery of FP into the agar gel to more than ten times its former level, in spite of the fact that it had no effect on systemic delivery. Bradykinin strengthened systemic delivery slightly, without changing the quantity of FP in the gel. IPM increased only the systemic delivery of FP, as was the case with bradykinin, whereas the MEGW system markedly increased both the blood concentration and the quantity of FP in the gel (13 and 200 times, respectively). This technique has proven to be an effective tool for the quantitative evaluation of cutaneous disposition of a topically applied drug.

Improved nasal absorption of drugs using poly-L-arginine: effects of concentration and molecular weight of poly-L-arginine on the nasal absorption of fluorescein isothiocyanate-dextran in rats.

The effects of the concentration and molecular weight of poly-L-arginine (poly-L-Arg) on the in vivo nasal absorption of fluorescein isothiocyanate-labeled dextran (MW, 4 kDa, FD-4) in rats were studied. When poly-L-Arg with a range of different molecular weights (MW, 8.9, 45.5 and 92.0 kDa) was applied intranasally at various concentrations, the bioavailability (F(0-9 h)) of FD-4 increased with the increasing concentration of poly-L-Arg. The enhanced absorption was also dependent on the molar concentration, in that the poly-L-Arg with a higher molecular weight increased F(0-9 h) at a lower molar concentration. In addition, for each applied concentration, the poly-L-Arg exhibited a molecular weight-dependence as far as the enhancement of FD-4 absorption was concerned. On the other hand, the maximum absorption rate (MAR) of FD-4, calculated by means of a deconvolution method, tended to reach a maximum plateau level at a lower applied concentration for the poly-L-Arg with the highest molecular weight, but this plateau level was almost the same for poly-L-Arg with molecular weights of 45.5 and 92.0 kDa. Moreover, the simulated absorption profiles of FD-4 indicate that the degree of enhancement (the level of MAR and the subsequent reduction in the absorption rate) was dependent on the molecular weight of poly-L-Arg, while the effect of poly-L-Arg was maintained for a longer period, depending on the applied concentration, although the MAR was relatively similar. These results indicate that the molecular weight of poly-L-Arg appears to affect both the enhancing efficiency (absorption rate) and the time-frame of this enhancing effect, whereas the concentrations of each poly-L-Arg system applied only have an effect on the time-frame. These effects may also be associated with the charge density of a poly-L-Arg molecule.

Selective accumulation and tumoricidal effect of cisplatin suspended in viscous ethyl oleate on hepatic cancers in animals after intraarterial infusion.

The selective accumulation and tumoricidal effects of cisplatin after intra-arterial infusion suspended in viscous ethyl oleate (VEO) on hepatic cancers of AH 272 tumor-bearing rats and VX-2 tumor-bearing rabbits were compared with those of cisplatin suspensions in ethyl oleate (EO) and Lipiodol Ultra Fluide (LP). The viscosities of VEO, EO and LP were 120, 4, and 21 centipoise (cp) respectively. Complete in vitro release of cisplatin from EO and LP occurred within 24 h, whereas only about 25% of cisplatin was released from VEO over the same period. When EO or VEO containing 3H-oleic acid were infused into the hepatic artery of rat liver inoculated with AH 272 tumor cells, radioactivity in the tumor site was higher than that in normal liver. In the case of cisplatin, concentration ratios after the infusion of EO and VEO were almost the same as those of oily carriers. Similar results were obtained in rabbit liver inoculated with VX-2 tumor cells. Cisplatin concentration in the tumor site seven days after intra-arterial infusion of VEO suspension was 5- and 1.7-fold higher, respectively, than that after EO and LP suspensions. The tumoricidal effect of cisplatin in VEO suspension on AH 272 tumor-bearing rats was higher than that after cisplatin solution and EO and LP suspensions, while VX-2 tumor growth was inhibited by the infusion of all cisplatin-containing oily carriers. VEO suspension thus appears very promising in intra-arterial infusion therapy.

Species differences in percutaneous absorption of nicorandil.

The species difference in skin permeability, Kp, of nicorandil was determined by using excised skin samples from hairless mouse, hairless rat, guinea-pig, dog, pig, and human. The Kp value of nicorandil in hairless mice was the greatest among the six species, and those in pigs and humans were in good agreement. To clarify the reasons for the species difference, various skin characteristics in each species were measured. It was suggested that the difference of skin surface lipids in each species affected the partitioning of nicorandil from vehicle to stratum corneum, and that such a difference would be a main factor for the species difference in nicorandil permeability. Since pig and human skins had similar surface lipids, barrier thickness, and morphological aspects, percutaneous absorption studies using excised pig skin samples would be useful for the estimation of in vitro human skin permeation behavior.

Mechanism of skin penetration-enhancing effect by laurocapram.

In order to clarify the mechanism of action of laurocapram (Azone) on the skin permeation of drugs, the following experiments were done. First, the effect of Azone on the skin components was compared with that of other penetration enhancers. Azone markedly fluidized liposomal lipids (as a model lipid system) compared with other enhancers. Ethanol extracted large amounts of the stratum corneum lipids, whereas Azone did not. These results suggest that the effect of Azone on the lipids in the stratum corneum is not the same as that of ethanol. In addition, ethanol increased the amount of free sulfhydryl (SH) group of keratin in the stratum corneum, whereas Azone did not directly affect the stratum corneum protein. Azone increased water content in the stratum corneum, as measured by skin conductance. This effect might be a reason for the action of Azone. For further understanding, the enhancing effects of Azone on the skin permeation of several model compounds (alcohols, sugars, and inorganic ions) were compared with the effects of pretreatment with distilled water, which was thought to increase water-holding capacity, and pretreatment with ethanol, which was thought to affect the lipids and protein in the skin barrier (i.e., stratum corneum). Pretreatment with water or ethanol enhanced skin permeation of hydrophilic compounds, whereas they decreased that of octanol, a hydrophobic compound. The tendency of Azone to increase or decrease the skin permeation rate of most compounds was similar to that of pretreatment with water or ethanol. However, the effect of Azone on the skin permeation of inorganic ions was relatively low, whereas that of pretreatment with water or ethanol was high.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of 1-dodecylazacycloheptan-2-one (Azone) on the topical therapy of cutaneous herpes simplex virus type 1 infection in hairless mice with 2',3'-di-O-acetyl-9-beta-D-arabinofuranosyladenine and 5'-O-valeryl-9-beta-D-arabinofuranosyladenine.

The predictive value of a recently developed physical model was tested in the topical treatment of cutaneous infections caused by herpes simplex virus type 1 in hairless mice with two ester prodrugs of 9-beta-D-arabinofuranosyladenine (ara-A) (1). The tests were conducted with 2',3'-di-O-acetyl-ara-A (4) and 5'-O-valeryl-ara-A (3) topically applied with and without 15% 1-dodecylazacycloheptan-2-one (2) (Azone), a percutaneous penetration enhancer. In addition to the in vivo studies, in vitro diffusion cell experiments with excised, full-thickness skin from hairless mice were conducted to determine the penetration enhancement effects of 2. As previously observed, 2 was able to induce remarkably large (100- to 1000-fold) flux enhancements in these in vitro experiments. Consistent with predictions based on the physical model studies, formulations of 3 and 4 without 2 had little or no influence on the pathogenesis of the herpes simplex virus type 1 infections; when 2 was present in the formulations, both 3 and 4 had dramatic therapeutic effects consistent with the predictions made with the physical model. Prodrug 4 with 2 was especially efficacious in the prevention of virus-induced lesions and in the survival of all animals. Similar results were obtained with acyclovir plus 2 in this model system.

Kinetic analysis on the in vitro cytotoxicity using Living Skin Equivalent for ranking the toxic potential of dermal irritants.

The extent of cytotoxicity injured by several skin irritants was kinetically measured and analyzed in a three-dimensional cultured human skin model, Living Skin Equivalent-002 (LSE). Colorimetric thiazoyl blue (MTT) conversion assay was selected as a cytotoxicity assay, and olive oil (OO), lactic acid (LA), Triton X-100 (TX) and sodium lauryl sulfate (SLS) were evaluated as model irritants. OO had almost no effect on the viability of LSE. When the other irritants were applied on the full-thickness LSE, two first-ordered decreasing phases, initial slow and following rapid phases, were found in the viability of LSE. LA and TX showed a bigger difference between the slow and rapid rates than SLS to show an inflection. The inflection time point from the slow to rapid rate was dependent on the kind and concentration of irritants applied. The higher the concentration of irritants applied, the more rapid the inflection point was observed. When LA and SLS were applied on the stratum corneum-stripped LSE, on the other hand, viability was mono-exponentially decreased with time. LA, TX and SLS probably decrease the barrier function of the stratum corneum to increase the rate of cytotoxicity during the irritant application. Interestingly, the rate of cytotoxicity on the stripped skin was similar to the late rapid rate on the full-thickness skin in LA not in SLS. These results suggest that cytotoxicity of skin irritants on the full-thickness LSE can be represented by two first-order kinetics, and that the skin irritation rate is closely related by the barrier function of skin as well as the application concentration and intrinsic toxicity of irritants.

Electric field analysis on the improved skin concentration of benzoate by electroporation.

The objective in the present study was to understand the relationship between the increased skin concentration of benzoate as a model drug after topical application of its sodium salt and the electric field intensity produced in the skin barrier, the stratum corneum, by electroporation. A piece of excised abdominal hairless rat skin was set in a Franz type diffusion cell, and 0.5% sodium benzoate and physiological saline were applied to the stratum corneum and dermis sides, respectively. Two needle electrodes made of Ag were connected to an electrical power source, which produced exponentially decaying pulses. The electrodes were placed on the skin surface with a distance of 0.5 cm between both electrodes. After the 4 h passive permeation experiment, an electrical pulse was applied to the rat skin at 300 V every minute for 10 min. The skin was then removed from the diffusion cell, and the amounts of benzoate in different positions of the skin specimen were measured. Field intensity generated in the stratum corneum by electroporation was determined by a finite element method using a computer program. The amounts of benzoate at different sites in the skin were almost proportional to the mean field intensity in the corresponding stratum corneum. These results suggested that the enhancing effect of electroporation can be evaluated by the field intensity more directly than the application voltage.

Effect of poly-L-arginine on the nasal absorption of FITC-dextran of different molecular weights and recombinant human granulocyte colony-stimulating factor (rhG-CSF) in rats.

The effect of poly-L-arginine (poly-L-Arg) on the in vivo nasal absorption of FITC-dextrans with a mean molecular weight ranging from 4.3 to 167 kDa and recombinant human granulocyte colony-stimulating factor (rhG-CSF) in rats were studied. When FITC-dextrans were co-administered intranasally with 1.0 w/v% poly-L-Args of different molecular weight (MW, ca. 45.5 and 92 kDa, poly-L-Arg (50) and poly-L-Arg (100)), the bioavailability (F(infinity)) increased markedly compared with that after administration of FITC-dextran alone. However, the F(infinity) decreased exponentially with the increasing molecular weight of FITC-dextrans. There was no significant difference between the enhanced nasal absorption of FITC-dextrans achieved by the co-administration of poly-L-Arg (50) and poly-L-Arg (100). Moreover, the relationship between the F(infinity) and the molecular weight of FITC-dextrans indicated that the molecular weight of protein drugs, which exhibited efficient absorption with poly-L-Arg, was about 20 kDa, when the lower limit of bioavailability for developing a potent transnasal delivery system was assumed to be about 10%. Indeed, the nasal absorption of rhG-CSF, which has a molecular weight of 18.8 kDa, was also increased after co-administration of 1.0 w/v% poly-L-Arg (50) and the F(infinity) was about 11%. It seems likely that poly-L-Arg can be used to provide adequate nasal absorption of various protein drugs which have a molecular weight of about 20 kDa, thereby allowing the successful development of a variety of transnasal drug delivery systems.

Screening of cationic compounds as an absorption enhancer for nasal drug delivery.

Several cationic compounds were screened as potential nasal absorption enhancers to increase intranasal absorption of a model drug, fluorescein isothiocyanate labeled dextran (MW 4.4 kDa, FD-4), without nasal membrane damage in rats. Their effects were compared with those of classical enhancers. Various cationic compounds (poly-L-arginines with different molecular weights (MW 8.9, 45.5 and 92.0 kDa, poly-L-Arg (10), (50) and (100), respectively), L-arginine (L-Arg), L-lysine (L-Lys), and cetylpyridinium chloride (CPCL) were evaluated. Of the cationic compounds, poly-L-Arg and CPCL greatly enhanced the intranasal absorption of FD-4, as did chitosan, a cationic polysaccharide which has been reported to show a great effect on the transnasal delivery of peptide and protein drugs. The enhancing intensity by poly-L-Arg was dependent on its molecular weight. Rank order of the enhancing ratio, calculated from the AUC ratio for the enhancer treatment against the untreatment, was 0.5% poly-L-Arg (100) congruent with0.5% sodium dodecylsulfate congruent with0.5% CPCL?0.5% poly-L-Arg (50)?0.5% sodium deoxycholate congruent with0.5% sodium taurodihydrofusidate?0.5% polyoxyethylene-9-lauryl ether congruent with0.5% lysophosphatidylcholine?0.5% chitosan congruent with0.5% poly-L-Arg (10)>/=10% L-Arg congruent with10% L-Lys?0.5% sodium glycocholate congruent with0.5% sodium taurocholate congruent with0.5% EDTA. Only the poly-L-Args represented almost the same degree of hemolysis of cationic compounds compared with pH 7.0 phosphate buffered saline in the rat erythrocyte lysis experiment. The enhancing ratio by classical enhancers correlated with leaching of protein, phospholipids and LDH from isolated rabbit nasal mucosa. CPCL also fell on the regression lines between the enhancing ratio and their degree of leaching from classical enhancers. In contrast, the enhancing intensities by poly-L-Arg (10), (50) and (100) were greatly shifted from the regression line: the amount of leaching was markedly low in spite of a great enhancement of FD-4 absorption. These findings suggest that of the assessed enhancers only the poly-L-Args enhance the transnasal delivery of high molecular substances without severe damage to the nasal mucosal membrane. Poly-L-Arg is therefore a promising candidate having a good balance between enhancing activity and safety for nasal peptide and protein delivery.

Non-invasive sampling of lactic acid ions by iontophoresis using chloride ion in the body as an internal standard.

Non-invasive sampling of lactic acid, as a model endogenous compound, through hairless rat skin by iontophoresis was investigated using a two-chamber iontophoretic diffusion cell equipped with platinum electrodes and a pulse depolarization iontophoretic system. Chloride ion in the body was used as an internal standard. First, an in vitro experiment on the permeation of lactate and chloride ions through hairless rat skin was carried out to determine the flux ratio of these ions. The cathode side of the cell (dermis side) was filled with physiological saline containing lactic acid (0.5556, 1.111, 1.667 or 2.222 mmol cm-3) and the anode side (epidermis side) with phosphate buffer (pH 7.4). The amount of lactate and chloride ion permeated from the dermis side to the epidermis side through the skin at a constant current of 3.0 mA was determined using an automatic lactic acid analyser and high-performance ion chromatography, respectively. For construction of a calibration curve of lactic acid in the dermis side, the ionic mobility ratio of lactic acid/chloride ion (UCl/Ulac) was determined using a computer simulation program from the flux ratio of lactic acid and chloride ion and the applied concentration of lactic acid in the dermis side. Second, an in vitro non-invasive sampling experiment of lactic acid through rat skin was carried out at a constant current of 2.0 or 3.0 mA and 2.222 or 1.111 mmol cm-3 of lactic acid in the dermis side, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Optimum threshold values of 201Tl SPET in the determination of the left ventricular border and extent of myocardial infarction.

The aim of this study was to determine the optimum threshold value of the left ventricular border and the extent of myocardial infarction using quantitative 201Tl single photon emission tomography (SPET). We used the unfolded map method to determine the size of the left ventricle and the extent of myocardial infarction in 10 patients, because it has been shown to be superior to the conventional polar map method. The relative differences in the size of the left ventricle and extent of infarction between 201Tl SPET and post-mortem examination were calculated. The optimum threshold value was determined when the relative difference = 0%. There was an excellent correlation between scintigraphic and post-mortem left ventricular size at a threshold value of 53% (r = 0.91, P < 0.001); an excellent correlation was also observed between scintigraphic and post-mortem infarct size at a threshold value of 55% (r = 0.93, P < 0.03). The optimum threshold value in determining left ventricular size using 201Tl SPET is 53% and that in determining infarct size is 55%.

A disintegration test for vaginal tablets: comparison with BP test.

To improve the disintegration test for vaginal tablets described in the British Pharmacopoeia (BP), a monitoring apparatus was added, and tested with seven effervescent and five non-effervescent tablets. A tablet was placed on the metal disc of the BP disintegration apparatus, and the guided plate was placed on the tablet. The guided plate moved downward smoothly in a cylinder as the tablet disintegrated. The movement was recorded by using a kymograph. The end-point and process of disintegration of the tablet were automatically recorded and the results obtained suggest that the modified test is a useful tool for the quality control of vaginal tablets.

Prediction of skin permeability of drugs: comparison of human and hairless rat skin.

Relationships between skin permeability and physicochemical properties of drugs were examined to establish a predictive method for the steady-state permeation rate of drugs through human skin. Human skin permeation properties fell into two categories: one in which the permeability coefficient is correlated to the partition coefficient, revealed with lipophilic drugs; and the other in which the permeability coefficients are almost constant, shown with hydrophilic drugs. The stratum corneum, the main barrier in skin, could be considered as a membrane with two parallel permeation pathways: lipid and pore pathways, and an equation for predicting the steady-state permeation rate of drugs was derived. The skin permeabilities of drugs for man were compared with those for hairless rat. The species difference in skin permeability found was suggested to be due to the difference in skin permeation pathways, since lipid content and water uptake of the stratum corneum varied between human and hairless rat skin.

Drug permeation through the three layers of the human nail plate.

The in-vitro permeation characteristics of a water soluble model drug, 5-fluorouracil, and a poorly water soluble model drug, flurbiprofen, were investigated through three layers of the human nail plate (namely, the dorsal, intermediate and ventral nail plates), using a modified side-by-side diffusion cell. The dorsal-filed nail plate, the ventral-filed nail plate and the dorsal-and-ventral-filed nail plate were prepared to known thicknesses and then used with the full-thickness nail plate to investigate the permeation characteristics of each single layer. Most of the lipids in the human nail plate were found in the dorsal and ventral layers. The rank orders of the permeation fluxes for 5-fluorouracil and flurbiprofen were both: dorsal-and-ventral-filed nail plate > dorsal-filed nail plate > ventral-filed nail plate > full-thickness nail plate. With respect to 5-fluorouracil permeation through each single layer, the permeability coefficient of the intermediate layer was higher than those of other single layers. However in the case of flurbiprofen, the permeability coefficient of the ventral layer was higher than other single layers. The diffusion coefficients of 5-fluorouracil and flurbiprofen in the dorsal layer were the lowest of any single layer. The drug concentration in each layer was estimated using each respective permeation parameter. The drug concentration in the nail plate was observed to be dependent on the solubility and the flux of the drug. From these findings, we suggest that the human nail plate behaves like a hydrophilic gel membrane rather than a lipophilic partition membrane and that the upper layer functions as the main nail barrier to drug permeation through its low diffusivity against the drugs.

Prediction of the in-vitro human skin permeability of nicorandil from animal data.

A method for estimating the in-vitro permeability of human skin to drugs, based on in-vitro permeation studies using animal skins, has been developed. The skins from hairless rats, guinea-pigs, dogs and pigs were used, with nicorandil and deionized water as model drug and solvent in a drug-donor compartment. Diffusion coefficients through the skin barrier, D, and partition coefficients from the drug-donor compartment to skin, K, of the drug, in each species, were calculated by curve-fitting the in-vitro permeation data to a diffusion equation describing the drug permeation through a homogeneous membrane, using a non-linear least squares method. Each barrier thickness, L, was measured microscopically from microtomed skin sections. A positive relationship was found between the skin permeability, Kp, and K value among the four species, but species differences in the D and L values were small in spite of the Kp values being different among the four species. A positive correlation was also observed between the calculated and experimental K values among the four species, and hence it was suggested that the main factor for the species difference in the skin permeability of nicorandil would be the difference in partitioning of the drug from vehicle to stratum corneum. As a result, it has become feasible to predict and estimate skin permeability of nicorandil in humans by substituting each parameter, extrapolated from the animal skin permeation data and partition experiments, in the diffusion equation.